A conventional bistable liquid crystal display (LCD) has two stable liquid crystal (LC) configurations that can exist with no applied voltage. Switching between the two stable LC configurations is achieved via the application of a suitable voltage waveform, and the voltage waveform is not required to maintain either stable state but only to switch between the stable states. When combined with other optical components (e.g., polarizers), the two stable LC configurations have two optically distinct states. Because the voltage waveform is not required to maintain either stable state but only to switch between the stable states, no power is consumed in a stable LC configuration, and consequently bistable LCDs are attractive for their low power consumption. Bistable LCDs have been previously disclosed, for example, in U.S. Pat. No. 4,333,708 (Boyd et al., issued Jun. 8, 1982), U.S. Pat. No. 9,280,018 (Mottram et al., issue Mar. 8, 2016), U.S. Pat. No. 5,796,459 (Bryan-Brown et al., issued Aug. 18, 1998), and U.S. Pat. No. 6,903,790 (Kitson et al., issued Jun. 7, 2005).
Generally, a zenithal bistable display (ZBD) device includes a zenithal bistable alignment surface that is an LC alignment surface that can adopt either a substantially vertically aligned state or a substantially planar aligned state with respect to the LC molecules at the alignment surface. LCDs described in U.S. Pat. No. 6,784,968B1 have at least a first zenithally bistable alignment surface located on an opposite side of the LC layer from a monostable alignment surface (which has only a single alignment state). In other embodiments, U.S. Pat. No. 6,784,968B1 also discloses an LCD that has two zenithally bistable alignment surfaces facing or opposing each other with the LC layer disposed between the two zenithally bistable alignment surfaces. An LCD with two zenithally bistable alignment surfaces may have four stable LC configurations that each can exist with no applied voltage, by virtue of the different combinations of the horizontal and vertical alignment states of the two zenithally bistable alignment surfaces.
ZBD devices of the type described above are pixelated. As such, each pixel may be separately addressed with a driving voltage waveform to place a given pixel in a given LC configuration (and corresponding optical state), which as referenced above is a stable state that will persist when the voltage is removed. Subsequently, a suitable driving voltage waveform may be applied to switch the given pixel to another one of the stable LC configurations. By selectively addressing the various pixels, different optical states applied to the various pixels can be combined into images that are visible to a viewer of the display device. Example conventional systems and methods of addressing ZBD devices are described, for example, in GB 2346978 (Jones et al., issued Dec. 5, 2001), U.S. Pat. No. 6,784,968B1 (Hughes et al., issued Aug. 31, 2004), and U.S. Pat. No. 8,130,186B2 (Jones, issued Mar. 6, 2012).
Integrated circuit “control chips” are known in the art that act as addressing devices that can supply the driving voltages for addressing pixelated display devices. Such chips are difficult to design and expensive to manufacture. Accordingly, certain standardized or stock chips are available that typically are employed in the display industry for addressing pixelated displays. Such stock chips, however, have proven to be deficient for driving ZBD devices because the available driving voltages that can be outputted from stock or conventional control chips are limited. Accordingly, stock control chips as typically employed may not have the scope of potential output driving voltages to achieve each of the multiple LC configurations that otherwise could be achieved in a ZBD device, and thus the corresponding multiple optical states are not fully realized.